ORCID Profile
0000-0001-5078-3689
Current Organisation
Université catholique de Louvain
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Publisher: Springer Science and Business Media LLC
Date: 26-04-2022
Abstract: The top quark pair production cross section is measured in proton-proton collisions at a center-of-mass energy of 5.02 TeV. The data were collected in a special LHC low-energy and low-intensity run in 2017, and correspond to an integrated luminosity of 302 pb − 1 . The measurement is performed using events with one electron and one muon of opposite charge, and at least two jets. The measured cross section is 60 . 7 ± 5 . 0 (stat) ± 2 . 8 (syst) ± 1 . 1 (lumi) pb. A combination with the result in the single lepton + jets channel, based on data collected in 2015 at the same center-of-mass energy and corresponding to an integrated luminosity of 27.4 pb − 1 , is then performed. The resulting measured value is 63 . 0 ± 4 . 1 (stat) ± 3 . 0 (syst+lumi) pb, in agreement with the standard model prediction of $$ {66.8}_{-3.1}^{+2.9} $$ 66.8 − 3.1 + 2.9 pb.
Publisher: Springer Science and Business Media LLC
Date: 02-2022
Abstract: Inclusive and differential cross sections of single top quark production in association with a Z boson are measured in proton-proton collisions at a center-of-mass energy of 13 TeV with a data s le corresponding to an integrated luminosity of 138 fb − 1 recorded by the CMS experiment. Events are selected based on the presence of three leptons, electrons or muons, associated with leptonic Z boson and top quark decays. The measurement yields an inclusive cross section of $$ {87.9}_{-7.3}^{+7.5}{\\left(\\mathrm{stat}\\right)}_{-6.0}^{+7.3}\\left(\\mathrm{syst}\\right) $$ 87.9 − 7.3 + 7.5 stat − 6.0 + 7.3 syst fb for a dilepton invariant mass greater than 30 GeV, in agreement with standard model (SM) calculations and represents the most precise determination to date. The ratio between the cross sections for the top quark and the top antiquark production in association with a Z boson is measured as $$ {2.37}_{-0.42}^{+0.56}{\\left(\\mathrm{stat}\\right)}_{-0.13}^{+0.27}\\left(\\mathrm{syst}\\right) $$ 2.37 − 0.42 + 0.56 stat − 0.13 + 0.27 syst . Differential measurements at parton and particle levels are performed for the first time. Several kinematic observables are considered to study the modeling of the process. Results are compared to theoretical predictions with different assumptions on the source of the initial-state b quark and found to be in agreement, within the uncertainties. Additionally, the spin asymmetry, which is sensitive to the top quark polarization, is determined from the differential distribution of the polarization angle at parton level to be 0 . 54 ± 0 . 16 (stat) ± 0 . 06 (syst), in agreement with SM predictions.
Publisher: Springer Science and Business Media LLC
Date: 14-04-2022
Abstract: A search has been performed for heavy resonances decaying to ZZ or ZW and for axion-like particles (ALPs) mediating nonresonant ZZ or ZH production, in final states with two charged leptons ( ℓ = e , μ) produced by the decay of a Z boson, and two quarks produced by the decay of a Z, W, or Higgs boson H. The analysis is sensitive to resonances with masses in the range 450 to 2000 GeV. Two categories are defined corresponding to the merged or resolved reconstruction of the hadronically decaying boson. The search is based on data collected during 2016–2018 by the CMS experiment at the LHC in proton-proton collisions at a center-of-mass energy of 13 TeV, corresponding to an integrated luminosity of 138 fb − 1 . No significant excess is observed in the data above the standard model background expectation. Upper limits on the production cross section of heavy, narrow spin-2 and spin-1 resonances are derived as functions of the resonance mass, and exclusion limits on the production of bulk graviton particles and W′ bosons are calculated in the framework of the warped extra dimensions and heavy vector triplet models, respectively. In addition, upper limits on the ALP-mediated diboson production cross section and ALP couplings to standard model particles are obtained in the framework of linear and chiral effective field theories. These are the first limits on nonresonant ALP-mediated ZZ and ZH production obtained by the LHC experiments.
Publisher: Springer Science and Business Media LLC
Date: 11-04-2022
Abstract: A search for long-lived particles decaying into muon pairs is performed using proton-proton collisions at a center-of-mass energy of 13 TeV, collected by the CMS experiment at the LHC in 2017 and 2018, corresponding to an integrated luminosity of 101 fb − 1 . The data sets used in this search were collected with a dedicated dimuon trigger stream with low transverse momentum thresholds, recorded at high rate by retaining a reduced amount of information, in order to explore otherwise inaccessible phase space at low dimuon mass and nonzero displacement from the primary interaction vertex. No significant excess of events beyond the standard model expectation is found. Upper limits on branching fractions at 95% confidence level are set on a wide range of mass and lifetime hypotheses in beyond the standard model frameworks with the Higgs boson decaying into a pair of long-lived dark photons, or with a long-lived scalar resonance arising from a decay of a b hadron. The limits are the most stringent to date for substantial regions of the parameter space. These results can be also used to constrain models of displaced dimuons that are not explicitly considered in this paper.
Publisher: Springer Science and Business Media LLC
Date: 02-05-2012
Abstract: A search for new heavy resonances decaying to a pair of Higgs bosons (HH) in proton-proton collisions at a center-of-mass energy of 13 TeV is presented. Data were collected with the CMS detector at the LHC in 2016–2018, corresponding to an integrated luminosity of 138 fb − 1 . Resonances with a mass between 0.8 and 4.5 TeV are considered using events in which one Higgs boson decays into a bottom quark pair and the other into final states with either one or two charged leptons. Specifically, the single-lepton decay channel $$ \\mathrm{HH}\\to \\mathrm{b}\\overline{\\mathrm{b}}{\\mathrm{WW}}^{\\ast}\\to \\mathrm{b}\\overline{\\mathrm{b}}\\ell v\\mathrm{q}{\\overline{\\mathrm{q}}}^{\\prime } $$ HH → b b ¯ WW ∗ → b b ¯ ℓ v q q ¯ ′ and the dilepton decay channels $$ \\mathrm{HH}\\to \\mathrm{b}\\overline{\\mathrm{b}}{\\mathrm{WW}}^{\\ast}\\to \\mathrm{b}\\overline{\\mathrm{b}}\\ell v\\ell v $$ HH → b b ¯ WW ∗ → b b ¯ ℓ v ℓ v and $$ \\mathrm{HH}\\to \\mathrm{b}\\overline{\\mathrm{b}}\\uptau \\uptau \\to \\mathrm{b}\\overline{\\mathrm{b}}\\ell vv\\ell vv $$ HH → b b ¯ ττ → b b ¯ ℓ vv ℓ vv are examined, where ℓ in the final state corresponds to an electron or muon. The signal is extracted using a two-dimensional maximum likelihood fit of the $$ \\mathrm{H}\\to \\mathrm{b}\\overline{\\mathrm{b}} $$ H → b b ¯ jet mass and HH invariant mass distributions. No significant excess above the standard model expectation is observed in data. Model-independent exclusion limits are placed on the product of the cross section and branching fraction for narrow spin-0 and spin-2 massive bosons decaying to HH. The results are also interpreted in the context of radion and bulk graviton production in models with a warped extra spatial dimension. The results provide the most stringent limits to date for X → HH signatures with final-state leptons and at some masses provide the most sensitive limits of all X → HH searches.
Publisher: Springer Science and Business Media LLC
Date: 03-05-2022
Abstract: Results are presented from a search for physics beyond the standard model in proton-proton collisions at $$ \\sqrt{s} $$ s = 13 TeV in channels with two Higgs bosons, each decaying via the process H → b $$ \\overline{\\mathrm{b}} $$ b ¯ , and large missing transverse momentum. The search uses a data s le corresponding to an integrated luminosity of 137 fb − 1 collected by the CMS experiment at the CERN LHC. The search is motivated by models of supersymmetry that predict the production of neutralinos, the neutral partners of the electroweak gauge and Higgs bosons. The observed event yields in the signal regions are found to be consistent with the standard model background expectations. The results are interpreted using simplified models of supersymmetry. For the electroweak production of nearly mass-degenerate higgsinos, each of whose decay chains yields a neutralino $$ \\left({\\overset{\\sim }{\\upchi}}_1^0\\right) $$ χ ~ 1 0 that in turn decays to a massless goldstino and a Higgs boson, $$ \\left({\\overset{\\sim }{\\upchi}}_1^0\\right) $$ χ ~ 1 0 masses in the range 175 to 1025 GeV are excluded at 95% confidence level. For the strong production of gluino pairs decaying via a slightly lighter $$ \\left({\\overset{\\sim }{\\upchi}}_2^0\\right) $$ χ ~ 2 0 to H and a light $$ \\left({\\overset{\\sim }{\\upchi}}_1^0\\right) $$ χ ~ 1 0 , gluino masses below 2330 GeV are excluded.
Publisher: IOP Publishing
Date: 03-2022
DOI: 10.1088/1748-0221/17/03/P03014
Abstract: Many measurements at the LHC require efficient identification of heavy-flavour jets, i.e. jets originating from bottom (b) or charm (c) quarks. An overview of the algorithms used to identify c jets is described and a novel method to calibrate them is presented. This new method adjusts the entire distributions of the outputs obtained when the algorithms are applied to jets of different flavours. It is based on an iterative approach exploiting three distinct control regions that are enriched with either b jets, c jets, or light-flavour and gluon jets. Results are presented in the form of correction factors evaluated using proton-proton collision data with an integrated luminosity of 41.5 fb -1 at √s = 13 TeV, collected by the CMS experiment in 2017. The closure of the method is tested by applying the measured correction factors on simulated data sets and checking the agreement between the adjusted simulation and collision data. Furthermore, a validation is performed by testing the method on pseudodata, which emulate various mismodelling conditions. The calibrated results enable the use of the full distributions of heavy-flavour identification algorithm outputs, e.g. as inputs to machine-learning models. Thus, they are expected to increase the sensitivity of future physics analyses.
Publisher: Springer Science and Business Media LLC
Date: 08-04-2022
Abstract: A search for a heavy resonance decaying into a top quark and a W boson in proton-proton collisions at $$ \\sqrt{s} $$ s = 13 TeV is presented. The data analyzed were recorded with the CMS detector at the LHC and correspond to an integrated luminosity of 138 fb − 1 . The top quark is reconstructed as a single jet and the W boson, from its decay into an electron or muon and the corresponding neutrino. A top quark tagging technique based on jet clustering with a variable distance parameter and simultaneous jet grooming is used to identify jets from the collimated top quark decay. The results are interpreted in the context of two benchmark models, where the heavy resonance is either an excited bottom quark b ∗ or a vector-like quark B. A statistical combination with an earlier search by the CMS Collaboration in the all-hadronic final state is performed to place upper cross section limits on these two models. The new analysis extends the lower range of resonance mass probed from 1.4 down to 0.7 TeV. For left-handed, right-handed, and vector-like couplings, b ∗ masses up to 3.0, 3.0, and 3.2 TeV are excluded at 95% confidence level, respectively. The observed upper limits represent the most stringent constraints on the b ∗ model to date.
Publisher: American Physical Society (APS)
Date: 09-2023
Publisher: Springer Science and Business Media LLC
Date: 08-04-2022
Abstract: A search is presented for a right-handed W boson (W R ) and a heavy neutrino (N), in a final state consisting of two same-flavor leptons (ee or μμ) and two quarks. The search is performed with the CMS experiment at the CERN LHC using a data s le of proton-proton collisions at a center-of-mass energy of 13 TeV corresponding to an integrated luminosity of 138 fb − 1 . The search covers two regions of phase space, one where the decay products of the heavy neutrino are merged into a single large-area jet, and one where the decay products are well separated. The expected signal is characterized by an excess in the invariant mass distribution of the final-state objects. No significant excess over the standard model background expectations is observed. The observations are interpreted as upper limits on the product of W R production cross sections and branching fractions assuming that couplings are identical to those of the standard model W boson. For N masses m N equal to half the W R mass $$ {m}_{{\\mathrm{W}}_{\\mathrm{R}}} $$ m W R ( m N = 0 . 2 TeV), $$ {m}_{{\\mathrm{W}}_{\\mathrm{R}}} $$ m W R is excluded at 95% confidence level up to 4.7 (4.8) and 5.0 (5.4) TeV for the electron and muon channels, respectively. This analysis provides the most stringent limits on the W R mass to date.
Publisher: Elsevier BV
Date: 11-2022
Publisher: Springer Science and Business Media LLC
Date: 20-10-2022
DOI: 10.1038/S41567-022-01682-0
Abstract: Since the discovery of the Higgs boson in 2012, detailed studies of its properties have been ongoing. Besides its mass, its width—related to its lifetime—is an important parameter. One way to determine this quantity is to measure its off-shell production, where the Higgs boson mass is far away from its nominal value, and relating it to its on-shell production, where the mass is close to the nominal value. Here we report evidence for such off-shell contributions to the production cross-section of two Z bosons with data from the CMS experiment at the CERN Large Hadron Collider. We constrain the total rate of the off-shell Higgs boson contribution beyond the Z boson pair production threshold, relative to its standard model expectation, to the interval [0.0061, 2.0] at the 95% confidence level. The scenario with no off-shell contribution is excluded at a p -value of 0.0003 (3.6 standard deviations). We measure the width of the Higgs boson as $${{{\\varGamma }}}_{{{{{{\\rm{H}}}}}}}={3.2}_{-1.7}^{+2.4}\\,{{{{{\\rm{MeV}}}}}}$$ Γ H = 3.2 − 1.7 + 2.4 MeV , in agreement with the standard model expectation of 4.1 MeV. In addition, we set constraints on anomalous Higgs boson couplings to W and Z boson pairs.
Publisher: Elsevier BV
Date: 12-2022
Publisher: Springer Science and Business Media LLC
Date: 14-04-2022
Abstract: A search for supersymmetry in events with two or three low-momentum leptons and missing transverse momentum is performed. The search uses proton-proton collisions at $$ \\sqrt{s} $$ s = 13 TeV collected in the three-year period 2016–2018 by the CMS experiment at the LHC and corresponding to an integrated luminosity of up to 137 fb − 1 . The data are found to be in agreement with expectations from standard model processes. The results are interpreted in terms of electroweakino and top squark pair production with a small mass difference between the produced supersymmetric particles and the lightest neutralino. For the electroweakino interpretation, two simplified models are used, a wino-bino model and a higgsino model. Exclusion limits at 95% confidence level are set on $$ {\\overset{\\sim }{\\upchi}}_2^0/{\\overset{\\sim }{\\upchi}}_1^{\\pm } $$ χ ~ 2 0 / χ ~ 1 ± masses up to 275 GeV for a mass difference of 10 GeV in the wino-bino case, and up to 205(150) GeV for a mass difference of 7.5 (3) GeV in the higgsino case. The results for the higgsino are further interpreted using a phenomenological minimal supersymmetric standard model, excluding the higgsino mass parameter μ up to 180 GeV with the bino mass parameter M 1 at 800 GeV. In the top squark interpretation, exclusion limits are set at top squark masses up to 540 GeV for four-body top squark decays and up to 480 GeV for chargino-mediated decays with a mass difference of 30 GeV.
Publisher: Springer Science and Business Media LLC
Date: 05-2022
DOI: 10.1140/EPJC/S10052-022-10315-Y
Abstract: Using a data s le of $$\\sqrt{s}=13\\,\\text {TeV}$$ s = 13 TeV proton-proton collisions collected by the CMS experiment at the LHC in 2017 and 2018 with an integrated luminosity of $$103\\text {~fb}^{-1}$$ 103 fb - 1 , the $$\\text {B}^{0}_{\\mathrm{s}} \\rightarrow \\uppsi (\\text {2S})\\text {K}_\\mathrm{S}^{0}$$ B s 0 → ψ ( 2S ) K S 0 and $$\\text {B}^{0} \\rightarrow \\uppsi (\\text {2S})\\text {K}_\\mathrm{S}^{0} \\uppi ^+\\uppi ^-$$ B 0 → ψ ( 2S ) K S 0 π + π - decays are observed with significances exceeding 5 standard deviations. The resulting branching fraction ratios, measured for the first time, correspond to $${\\mathcal {B}}(\\text {B}^{0}_{\\mathrm{s}} \\rightarrow \\uppsi (\\text {2S})K_\\mathrm{S}^{0})/{\\mathcal {B}}(\\text {B}^{0}\\rightarrow \\uppsi (\\text {2S})K_\\mathrm{S}^{0}) = (3.33 \\pm 0.69 (\\text {stat})\\, \\pm 0.11\\,(\\text {syst}) \\pm 0.34\\,(f_{\\mathrm{s}}/f_{\\mathrm{d}})) \\times 10^{-2}$$ B ( B s 0 → ψ ( 2S ) K S 0 ) / B ( B 0 → ψ ( 2S ) K S 0 ) = ( 3.33 ± 0.69 ( stat ) ± 0.11 ( syst ) ± 0.34 ( f s / f d ) ) × 10 - 2 and $${\\mathcal {B}}(\\text {B}^{0} \\rightarrow \\uppsi (\\text {2S})\\text {K}_\\mathrm{S}^{0} \\uppi ^{+} \\uppi ^{-})/ {\\mathcal {B}}(\\text {B}^{0} \\rightarrow \\uppsi (\\text {2S})\\text {K}^{0}_{\\mathrm{S}}) = 0.480 \\pm 0.013\\,(\\text {stat}) \\pm 0.032\\,(\\text {syst})$$ B ( B 0 → ψ ( 2S ) K S 0 π + π - ) / B ( B 0 → ψ ( 2S ) K S 0 ) = 0.480 ± 0.013 ( stat ) ± 0.032 ( syst ) , where the last uncertainty in the first ratio is related to the uncertainty in the ratio of production cross sections of $$\\hbox {B}^{0}_{\\mathrm{s}}$$ B s 0 and $$\\hbox {B}^{0}$$ B 0 mesons, $$f_{\\mathrm{s}}/f_{\\mathrm{d}}$$ f s / f d .
Publisher: Springer Science and Business Media LLC
Date: 19-01-2023
DOI: 10.1038/S41567-022-01838-Y
Abstract: Protons consist of three valence quarks, two up-quarks and one down-quark, held together by gluons and a sea of quark-antiquark pairs. Collectively, quarks and gluons are referred to as partons. In a proton-proton collision, typically only one parton of each proton undergoes a hard scattering – referred to as single-parton scattering – leaving the remainder of each proton only slightly disturbed. Here, we report the study of double- and triple-parton scatterings through the simultaneous production of three J/ ψ mesons, which consist of a charm quark-antiquark pair, in proton-proton collisions recorded with the CMS experiment at the Large Hadron Collider. We observed this process – reconstructed through the decays of J/ ψ mesons into pairs of oppositely charged muons – with a statistical significance above five standard deviations. We measured the inclusive fiducial cross-section to be $$27{2}_{-104}^{+141}\\,{{{\\rm{(stat)}}}}\\,\\pm 17\\,{{{\\rm{(syst)}}}}\\,{{{\\rm{fb}}}}\\,$$ 27 2 − 104 + 141 (stat) ± 17 (syst) fb , and compared it to theoretical expectations for triple-J/ ψ meson production in single-, double- and triple-parton scattering scenarios. Assuming factorization of multiple hard-scattering probabilities in terms of single-parton scattering cross-sections, double- and triple-parton scattering are the dominant contributions for the measured process.
Publisher: American Physical Society (APS)
Date: 10-10-2023
Publisher: Elsevier BV
Date: 09-2022
Publisher: Springer Science and Business Media LLC
Date: 02-2022
Abstract: A search for flavor-changing neutral current interactions of the top quark (t) and the Higgs boson (H) is presented. The search is based on a data s le corresponding to an integrated luminosity of 137 fb − 1 recorded by the CMS experiment at the LHC in proton-proton collisions at $$ \\sqrt{s} $$ s = 13 TeV. Events containing exactly one lepton (muon or electron) and at least three jets, among which at least two are identified as originating from the hadronization of a bottom quark, are analyzed. A set of deep neural networks is used for kinematic event reconstruction, while boosted decision trees distinguish the signal from the background events. No significant excess over the background predictions is observed, and upper limits on the signal production cross sections are extracted. These limits are interpreted in terms of top quark decay branching fractions ( $$ \\mathcal{B} $$ B ) to the Higgs boson and an up (u) or a charm quark (c). Assuming one nonvanishing extra coupling at a time, the observed (expected) upper limits at 95% confidence level are $$ \\mathcal{B} $$ B (t → Hu) 0 . 079 (0 . 11)% and $$ \\mathcal{B} $$ B (t → Hc) 0 . 094 (0 . 086)%.
No related grants have been discovered for Sandhya Jain.